2000 Audi S4 AutomaticFACTORY OEM SERVICE PROCEDURE

Data Transfer Between Engine Control Module & Can-Bus Capable Control Modules

WARNING: This page is about a different car, the 2002 Audi S4. However, it is still accessible from the selected car via links, so may be relevant.

Data is transferred between control modules through the CAN-bus system. CAN-bus refers to a network connecting various control modules. Data is transferred between modules serially (one module after the other), through CAN-bus network. If DTC testing suggests checking data exchange between ECM and CAN capable control modules perform following procedure:

  1. Connect VAS 5051 or equivalent scan tool to DLC. DLC is located behind cover under left side of steering column. See COMPONENT LOCATIONS  . Start engine. On scan tool, press "01" to select address word 01 - ENGINE ELECTRONICS. Press "Q" button to confirm input. Press "08" to select diagnostic function 08 - READ MEASURING VALUE BLOCK. Press "Q" button to confirm input, and go to next step.
    2. NOTE: Measuring value blocks 125 and 126 indicate control modules connected to powertrain data-BUS.
  2. On scan tool, press "125" to select DISPLAY GROUP 125. CAN capable control modules are displayed in display fields 1-4 of display group 125. NO INDICATION: indicates control module is not CAN capable. INDICATION 1: CAN capable control module is connected to databus. INDICATION 0: CAN capable control module is not connected to databus. Press "FORWARD ARROW" button to switch to display group 126. Observe display group 126 for CAN capable modules. On scan tool, press "06" to select diagnostic function 06 - END OUTPUT. Press "Q" button to confirm input, and go to next step.
  3. On scan tool, press "00" to select address word 00 - CHECK DTC MEMORY - COMPLETE SYSTEM. DTC memory of all OBD capable systems in the vehicle will be checked. When each control module responds with it's identification, scan tool display indicates number of stored DTCs, or NO MALFUNCTIONS RECOGNIZED. DTC stored in the system are indicated in sequence and printed out. VAG scan tool sends next address word. Go to next step.
  4. If malfunction related to powertrain databus or CAN-bus is indicated. Verify that ECM or other CAN capable control modules installed are appropriate for vehicle (check part number and coding). Check for poor or loose terminals in control module harness connectors. If problem is found, repair as necessary. If no problem is found, go to next step.
  5. Using stored DTCs and data link connectors wiring diagram, analyze which control modules are not communicating. See ENGINE PERFORMANCE and COMPUTER DATA LINES wiring diagram in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Use example in illustrations to determine non-communicating modules. See Fig 1 -Fig 3 .
    Fig 1: Example 1: Locating Non-Communicating Control Module
    G00077136Courtesy of AUDI OF AMERICA, INC.
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